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Public proof of conceptFix available

CVE-2021-21809

A public proof of concept exists; no exploitation attested.

  • Published2021-06-23
  • WeaknessCWE-78

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

A command execution vulnerability exists in the default legacy spellchecker plugin in Moodle 3.10. A specially crafted series of HTTP requests can lead to command execution. An attacker must have administrator privileges to exploit this vulnerabilities.

Timeline

dates in UTC
  1. 2021-06-2322:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-11-03 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-21809?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-21809?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD · OSV
Moodle
BranchAffectedFixed in
3.10= 3.10.0no fix published
moodle
BranchAffectedFixed in
3.10≥ 3.10.0, < 3.10.13.10.1
moodle/moodle
BranchAffectedFixed in
—all versionsno fix published

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • moodleUbuntu:Pro:18.04:LTSall versions · no fixed version listed
  • moodleUbuntu:Pro:16.04:LTSall versions · no fixed version listed

Vendor advisories

  • CVE-2021-21809 Red Hat Product Security

    moodle: specially crafted series of HTTP requests can lead to command execution

Full record on NVD

Fix

No fix published by the sources we read yet. NVD record

Detection

read 2026-11-02 22:42 UTC
Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
1 repository, unverifiedanldori/CVE-2021-21809
PoC-in-GitHub
Metasploit modules
1 moduleexploit/multi/http/moodle_spelling_path_rcerank: excellentModule metadata: Metasploit Framework, © Rapid7, Inc., BSD-3-Clause.
Metasploit Framework

Sources

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H
Published
2021-06-23
Last Modified
2026-06-17
NVD status
Modified
GitHub Advisory
GHSA-c7jj-vfmr-j9mj

Frequently asked questions

What is CVE-2021-21809?

A command execution vulnerability exists in the default legacy spellchecker plugin in Moodle 3.10. A specially crafted series of HTTP requests can lead to command execution. An attacker must have administrator privileges to exploit this vulnerabilities.

Is CVE-2021-21809 actively exploited?

Active exploitation of CVE-2021-21809 has not been confirmed. Its EPSS score was 24.2% on 2026-11-03, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-21809?

CVE-2021-21809 has a CVSS v3 base score of 9.1 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H.

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Sources for this record